| China has been the largest country for production, consumption and export trade of peanut (Arachis hypogaea L.) during the past decade. Peanut has been playing important role in assuring vegetable oil supply, increasing farmers'cash income and enhancing exportation trade. Recently, the peanut industry has been challenged with several constraints in which aflatoxin (AFT) contamination caused by Aspergillus flavus and A.parasiticus has been a crucial factor. Development of host resistance to A.flavus infection and AFT production is the most desirable approach for AFT contamination management. However, progress toward developing peanut variety with resistance to AFT contamination has been slow due to various reasons. Normally, the resistance to AFT contamination in peanut could be divided into resistance to A.flavus infection and resistance to AFT production, in which, the resistance to A.flavus infection mainly depends on the protective role of the seed testae but it could loss once the testae are damaged. So it is important to identify or develop peanut genotypes resistant to AFT production. Even a lot of work has been done on enhancing resistance to AFT production, several problems remain unsolved including: a) the resistance is controlled by minor effect genes with less stability, b) the available resistant peanut lines generally possess small seeds with low yield potential or low oil content, and c) the mechanism and inheritance of the resistance are not clear. Therefore, it is highly necessary to establish a new strategy for genetic improvement of resistance to AFT production. In this thesis, resistance to AFT production in recombinant inbred lines (RILs) derived from cross combinations consisting of parents with different genetic background was investigated. The objectives of this study were to assess the potential for improving resistance to AFT formation by accelerating concerned minor effect genes or locus, to study mechanisms of resistance to AFT production and to analyze relationship between the resistance and other major characters. The results obtained were as followings.(1) Through artificial inoculation with A. flavus, aflatoxins were quantitatively determined in 117 peanut recombinant inbred lines derived from a cross of"Yuanza 9102×Zhonghua 5". Significant variation of aflatoxin content was observed among the RILs and several recombinants with AFT less than the parental lines were identified, indicating that there was a feasible potential for improving the resistance to AFT formation by accelerating the concerned minor effect genes or locus. This conclusion was also verified in another group of advanced lines derived from a cross of K01-6×Kainong-30.(2) In addition to identification of AFT production resistance, some other agronomic and quality traits in the peanut lines were properly characterized. Consequently, the correlation analysis between the AFT content and other major traits was implemented. There was no significant correlation between the resistance to AFT formation and pod mass, oil content, protein content, oleic and linoleic content, and resistance to bacterial wilt (BW) caused by Ralstonia solanacearum, indicating that there is a potential for integrating resistance to AFT production with other important characters.(3) The activity of peroxides (POD), polyphenoloxidase (PPO), phenylalanine ammonialyase (PAL) and contents of lignin and chlorogenic acid in selected peanut genotypes with different resistance to AFT production were determined after inoculation with A.flavus. The results indicated that the activities of PAL, PPO and POD significantly increased after inoculation, and the increasing speed was related with the resistance level. The activity of all the enzymes involved in resistant peanut genotypes increased much rapidly than that of susceptible ones. Compared to un-inoculated control, the content of lignin and chlorogenic acid of the resistant and susceptible genotypes gradually increased after inoculation, and the accumulated content varied among different genotypes. The results verified that the mechanism of AFT resisitance in the recombined lines was similar to resistant control (Zhonghua 6).(4) Several elite peanut lines with large pod, high oil content and desirable resistance to both BW and AFT production were identified, and they could be used in further breeding.
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